(Reuters Health) - People who suffer from posttraumatic stress disorder (PTSD) and other stress-related psychiatric issues may be at higher risk for development of autoimmune diseases, a Swedish study suggests.

Researchers studied 106,464 people diagnosed with stress disorders. 126,652 of their siblings without stress disorders, and more than 1 million other individuals in the Swedish population who didn't have stress disorders.

During a median follow-up of 10 years, individuals with PTSD were 46% more likely to develop an autoimmune disorder, and more than twice as likely to develop at least three autoimmune disorders, compared to adults without stress disorders.

"Severe or prolonged emotional stress causes alterations in multiple bodily functions through dysregulation in the release of stress hormones," said lead study author Dr. Huan Song of the University of Iceland in Reykjav k and the Karolinska Institute in Stockholm, Sweden.

When PTSD patients took selective serotonin reuptake inhibitors (SSRIs) during their first year after diagnosis, however, their risk of developing autoimmune disorders appeared to decline.

PTSD patients who took SSRIs for at least 320 days that first year after diagnosis were 82% more likely to develop autoimmune disorders than individuals without stress disorders, the study found. When PTSD patients took SSRIs for 179 days or less, however, they had more than triple the risk of autoimmune disorders.

"The main message to patients suffering from severe emotional reactions after trauma or other life stressors is to seek treatment," Song said by email. "There are now several treatments, both medications and cognitive behavioral approaches, with documented effectiveness."

Previous research has linked stress disorders to an increased risk of autoimmune disorders, but much of this work has focused on men who developed PTSD related to military service, the research team noted in JAMA, online June 19.

Immune problems can often run in families, and studies to date also haven't offered a clear picture of how much shared parentage or life circumstances might explain the connection between stress and autoimmune disorders.

Roughly 9 in every 1,000 people diagnosed with stress disorders in the study developed autoimmune disorders each year, researchers calculated. That compares to about 6 in 1,000 people in the population without stress disorders, and 6.5 in 1,000 siblings.

"It's a bit surprising that there is not a big difference between siblings and general population," said Dr. Johnny Ludvigsson, a researcher at Linkoping University in Sweden who wasn't involved in the study.

"One would have expected more importance of genetic background," Ludvigsson said by email.

The connection between stress and autoimmune disorders was stronger for endocrine problems like diabetes and weaker for skin and blood conditions.

Still, the results offer fresh evidence of the complex ways the brain can influence the immune system, and visa versa, said Dr. Michael Eriksen Benros, head of research at the Mental Health Centre Copenhagen in Denmark.

"There clearly is bidirectional interplay between the immune system and the brain," Benros, who wasn't involved in the study, said by email.

"Long-term psychological stress can influence multiple bodily systems including stress hormone levels and the autonomic nervous system resulting in impairment of immune functioning," Benros added. "This can lead to increased autoimmune disease activity and trigger exacerbations of autoimmune diseases or make individuals more prone to acquiring infections that together with genetic factors are believed to be the main etiological factors for autoimmune diseases."